CRM_Utils_File::absoluteDirectory() - Make `$basePath` required

CRM_Utils_File::absoluteDirectory() - Make `$basePath` required

Previous versions interpreted `$basePath=NULL` to mean "default to `self::baseFilePath()`".
However, no code in the known `universe` relies on this interpretation, and
the `baseFilePath()` function is problematic/deprecated.

We could almost deprecate the entire function `absoluteDirectory()`;
however, it's fine to keep around: the semantics are reasonable if one
provides `$basePath`, and there is one active use-case in which
`Civi\Core\Paths` calls `absoluteDirectory()` with a suitable `$basePath`.